How long does the capacitor keep the A139 Pro 2-Ch powered?

[SPL15]

In process of laying out the wiring for an A139 Pro 2-Ch w/ BBMC PC8 & Cellink Neo Ext battery.

I'm wiring in a 30 amp DPDT relay to control +12 Vdc Power In to the PC8. With the extra set of relay contacts, I plan to toggle power for the A139 between car's electrical system & the BC8.
This is to eliminate the shallow battery cycling while the ignition is on & batteries fully charged, as well as to slightly speed up charge time by eliminating the Dash Cam load while charging, in addition to it being easy to do.

The split second the relay is switching from car's electrical system to the PC8's, there will be a brief power cut due to how a mechanical relay works (likely around 5 - 15mS).

I'm assuming the A139 Pro's internal cap will buffer this brief pause, else it'd be kind of useless / pointless to even have.
Anyone know roughly how long the cap can power the device running 2 channels, full res, max bitrate?

 

[marcusb]

The capacitor is only there, as far as I know, to perform a safe shut down and avoid corrupting videos. If the camera sees the power being cut, it'll probably shut down.

 

[SPL15]

Hmm... Might need to test this out on the bench then. I've got faster relay options that'll do several microseconds for switching time.

 

[kamkar]

Yes any dashcams on board power are just there to properly finalize last recording in case of a catastrophic event.
A very few battery cameras do have a larger than needed battery, so maybe 450 MAH, but not something i would rely on in any way.

Some dashcams with batteries ( nextbase ) do recommend charging the battery.
In all the years i have tested dashcams i have just put then in and go, but TBH i can recall having tested a single battery powered system, they have all been capacitor based.

 

[Vortex Radar]

Right the cap is primarily there to allow for a clean shutdown and closing/saving the video file. I don't know how long of a gap it allows for before turning itself off, but I suspect there's a bit of room built in to allow for things like voltage drops from a start/stop system and so on. Voltage drops are different from voltage cut-offs, of course, but ultimately I think you'd have to test it to find out for sure.

 

[SPL15]

I’m speculating / hoping (based on nothing) that there’s likely a bit of debounce for the +12 battery input dropout vs automated shutdown routine.

Easy enough to measure hold-up times once I receive the Dashcam & HK3-C cable. I’ve got programmable Keysight SMU’s & programmable loads that’ll work great for getting exact hold-up times at various voltage conditions.

If there’s issues, I’m betting I could probably get it working by simply adding some bulk capacitance to the HK3-C regulator, or making a basic Schottky diode isolator so power never drops out during switchover from car’s electrical system to battery & vice versa.

 

[SPL15]

Followup:

A139 Pro w/ HK3-C hardwire cable can reliably sustain a momentary power loss on the B+ (red) of around 150mS without triggering the auto-shutdown routine. This is plenty of time for a mechanical relay to switch over.
Same results for the Accessory (Yellow) connection.
175mS worked on both Batt+ & ACC, but there's very little buffer as the unit started intermittently changing status when dropout duration got to 180mS.

Automated test sequence using Keysight N6705C Modular Mainframe w/ N6784A SMU's:

1. 5.0 seconds at 14.4 Vdc
2. 0.150 Seconds @ 0.00 Vdc (Output shorted to Ground / Low Impedance)
3. 5.0 Seconds @ 12.8 Vdc
4. 0.150 Seconds @ 0.00 Vdc (Output shorted to Ground / Low Impedance)
5. Repeat for 1+ hour

Switching back & fourth between 14.4Vdc to 12.8 is closer to what will happen in actual application, as the switchover occurs when the ignition is either cut-off or turned on. In modern vehicles with push button start, the actual sequencing is a bit more complex; however, what was tested is what should be worst case scenario.

Couple of other interesting observations (Nothing remarkable):

• ACC sucks down appox 130mA continuous. Fortunately, ACC is only drawing current w/ ignition on, but could definitely be optimized for better overall efficiency.
• The A139 Pro draws a constant power regardless of input voltage, suggesting a well designed switching regulator: Meaning higher voltage = less current draw. Less input voltage = More current draw.
  • Parking Mode - 1 Channel w/ WiFi enabled: Approx 3.8 watts (Fluctuates between 3.55 - 3.9 watts)
  • Parking Mode - 1 Channel w/ WiFi disabled: Approx 3.2 watts (Fluctuates between 3.05 - 3.25 watts)
• Unit w/ 1 Channel draws approx 4.1 - 4.7mA when shutdown @ 12.8 Vdc (common AGM battery voltage when 100% charged)
  • Poses zero issues for moderate term storage while connected to car battery (should always connect car to charger w/ modern vehicles if stored for more than a few days)
  • Switching supply is still active when shutdown: Current reduces w/ higher voltage, increases w/ lower voltage (ie constant power output)
  • Current further reduces by fractions of a mA as unit cools down (Expected: Less capacitor leakage, less inductor resistive losses, etc)
  • Possible to manually turn unit on w/ ACC not connected to V+ (Does not appear to enter parking mode)
• My HK3-C cable shuts down power at 11.73 Volts @ the 11.8 Vdc cutoff setting